Effects of prohexadione-calcium on physiological characteristics and fruit quality of Chardonnay grape

Abstract: 【Objective】The quality of wine grape determines the quality of the wine. In the arid regions of the Northwest, low rainfall and the cool climate in spring and autumn shorten the growing period of grape. Intermediate and late maturity varieties often have problems of insufficient maturity, insufficient sugar content, and low yield, which seriously impact the sustainable development of the wine grape industry. Previous studies have shown that the exogenous spraying of natural or synthetic inducers, such as abscisic acid, gibberellin, methyl jasmonate, etc., can effectively guarantee crop nutrition supply, improve resistance, enhance photosynthesis, and ultimately achieve the production goal of high quality and high yield. Prohexadione-calcium (Pro-Ca) is a low-toxicity, artificially synthesized non-polluting plant growth regulator and is thought to promote plant growth and improve fruit quality. The experiment intended to use Pro-Ca effervescent granules (containing 5% effective Pro- Ca) for whole- tree spraying of Chardonnay grape to explore the impact of Pro-Ca on grape physiological characteristics and fruit quality, and to screen out the suitable application concentration, providing a theoretical basis for improving the quality of wine grape.【Methods】The experiment used 11- year- old trees of wine grape Chardonnay as materials. On the 22 d, 42 d, 62 d, and 82 d from the initial flowering, the leaves were sprayed with 200 mg·L-1 (T1), 400 mg·L^-1 (T2), 600 mg·L^-1 (T3), and 800 mg·L^-1 (T4) Pro-Ca so-lution, respectively. The distilled water was used as control. The content of photosynthetic pigments, chlorophyll fluorescence parameters, photosynthetic characteristics, protective enzyme activity, and fruit quality-related indicators were measured on the 25, 45, 65, 85, and 105 days (maturity stage) after the initial flowering.【Results】(1) The pro-Ca treatment could enhance the content of photosynthetic pigments in Chardonnay grape leaves, increase the net photosynthetic rate (Pn), and result in changes in the chlorophyll fluorescence parameters. The T3 treatment increased the chlorophyll a (Chl a), chlorophyll b (Chl b) content, and Pn, by 19.63%, 16.67%, and 20.13% respectively, compared with the control. On the 65, 85, and 105 days after the initial flowering, the T3 treatment enhanced the leaf transpiration rate (Tr) compared with control by 10.50%, 28.68%, and 8.64%, respectively. On the 45, 65, and 85 days after initial flowering, the T3 treatment significantly (p＜0.05) increased the leaf stomatal conductance (Gs) compared with the control by 24.69%, 15.26%, and 7.24%, respectively. The leaf intercellular CO2 concentration (Ci) in the T3 treatment was significantly (p＜0.05) higher than those of the other treatments on the 65 and 85 days after the initial flowering, with increases of 3.13% and 5.55%, respectively. The pro-Ca treatment increased the leaf parameters Fv/Fm, Y(Ⅱ), qP, qN, and ETR to varying degrees, while reducing the leaf non- photochemical quenching (NPQ). Among them, on the 25, 45, 85, and 105 days after the initial flowering, the T3 treatment significantly (p＜0.05) increased Fv/Fm by 11.01%, 13.93%, 6.60%, and 7.55%, respectively, compared with the control. On the 25, 45, 65, 85, and 105 days after the initial flowering, the T3 treatment significantly (p＜0.05) increased Y (Ⅱ) by 4.42%, 7.35%, 8.16%, 3.69%, and 6.32%, respectively, compared with the control. (2) The pro-Ca treatment reduced the accumulation of reactive oxygen species in the leaves and increased the activity of protective enzymes. On the 45 days after the initial flowering, the T3 treatment significantly (p＜0.05) reduced the hydrogen peroxide (H2O2) content. On the 65 and 85 days after the initial flowering, the T3 treatment decreased the production rate of superoxide anion (O2 ^- ) by 34.42% and 24.98%, respectively. On the 25, 45, and 85 days after the initial flowering, the T2 treatment showed the highest APX activity, with increases of 5.18%, 9.70%, and 15.26%, respectively, compared with control. The T3 treatment significantly (p＜0.05) increased CAT activity by 16.83%, 13.58%, and 31.70% on the 65, 85, and 105 days after the initial flowering, respectively. The T3 treatment significantly enhanced (p＜0.05) POD activity by 25.62%, 34.81%, 12.00%, and 27.26% on the 45, 65, 85, and 105 days after the initial flowering, respectively. The SOD activity in the leaves increased by 6.86%, 13.15%, 4.48%, and 14.43% on the 45, 65, 85, and 105 days after the initial flowering, respectively, in the T3 treatment compared with the control. (3) Pro-Ca treatment increased the content of soluble solids, titratable acidity, total phenols, and flavonoids in the berries. Among them, the T3 treatment showed the most significant enhancement, with increases of 12.12%, 8.77%, 4.37%, and 21.9%, respectively, compared with control. (4) The principal component analysis was conducted on 29 indicators, including the physiological characteristics of the leaves and fruit quality, with different treatments. The comprehensive evaluation of the effects of ProCa treatment on wine grapes revealed that leaf spray with 600 mg·L^-1 Pro-Ca iwould be the most suitable concentration.【Conclusion】In summary, the pro-Ca treatment can enhance the photosynthesis, antioxidant properties and fruit quality of Chardonnay grape. 600 mg·L-1 Pro-Ca treatment had the best effect.